Simple IAP System (SIS) Call back is not working (HandleSuccessfulPurchase is not called)

Hi All, I am using Simple IAP System (SIS) for in IAP.. every this is working.. but the call back is not coming to HandleSuccessfulPurchase .

Can any one Help..

Please find the log: 09-18 22:59:26.743 3202-3202/? D/OpenIAB-UnityPlugin﹕ Consumption finished. Purchase: PurchaseInfo(type:inapp): {"orderId":GPA.1309-9263-8474-27552,"packageName":com.G2GDN.MonsterBall,"productId":gemspacktest,"purchaseTime":1442597361683,"purchaseState":0,"developerPayload":,"token":imkdpdcoflceegnnkmgkfaap.AO-J1Ows3vtUX5niRwMBCGD7kRFO4mqka3pV3uCy946WbFUkTGUlP09VGznxjI6U3yOQxM7J8luFZ8-EqHJf9F_QSkfJg04RwtvaVYUOORfeB6ETbKFRrUKXtllnHd59vPXGz8wBIfJ7}, result: IabResult: 0, Successful consume of sku gemspacktest (response: 0:OK) 09-18 22:59:26.743 3202-3202/? D/OpenIAB-UnityPlugin﹕ Consumption successful. Provisioning. 09-18 22:59:26.812 3202-3230/? I/Unity﹕ NullReferenceException: Object reference not set to an instance of an object at SIS.IAPManager.ConsumeSucceeded (OnePF.Purchase prod) [0x00000] in :0 at OpenIABEventManager.OnConsumePurchaseSucceeded (System.String json) [0x00000] in :0